Trans and diff oil swap in 4KCSQ

Just got back from work trip, and finally got your post.
re: trans oil upgrade
What exactly should be changed with the oil upgrade ? Tranny and differetial
oil? Did Audi recommend Synthetic oil for these tranny's? The rear diffential,
or the center thing between the rear whells has been leaking something for a
little while, haven't had a chance to do a complete inspection yet. Does one
upgrade this to synthetic as well? How much oil should do the trick?
is this what you recommend for oil? What make was it.?
synthetic 85W-90.
Thanks in advance
Nick out